Determination of daughter ion formulas by multiple stages of mass spectrometry.

The ability to obtain daughter ion formulas via comparison of MS(n) spectra of parent ions containing only (12)C with those of parent ions with one (13)C (from the natural (13)C abundance) is shown for cases in which isobaric interferences with the (13)C-containing ion preclude the use of the conventional tandem mass spectrometric approach. This method allows the presence of isobaric daughter ions to be ascertained, and unexpected, complex dissociation pathways to be identified. A three-dimensional quadrupole ion trap is used for these experiments. Its high tandem mass spectrometry efficiency makes possible this type of experiment.